U.S. patent application number 13/838352 was filed with the patent office on 2013-09-19 for process for purification of produced water.
The applicant listed for this patent is Narendra Singh Bisht, Ravi Chidambaran, Pavan Raina. Invention is credited to Narendra Singh Bisht, Ravi Chidambaran, Pavan Raina.
Application Number | 20130240442 13/838352 |
Document ID | / |
Family ID | 49156669 |
Filed Date | 2013-09-19 |
United States Patent
Application |
20130240442 |
Kind Code |
A1 |
Chidambaran; Ravi ; et
al. |
September 19, 2013 |
PROCESS FOR PURIFICATION OF PRODUCED WATER
Abstract
We provide a process for treatment of produced water, including
but not limited to water produced by a "steam flood" process for
extraction of oil from oil sands, including the removal of color
from the water. This removal may be accomplished through addition
of color-removal polymers and flocculents. This process may also be
useful for other water treatment processes including reverse
osmosis and filtration.
Inventors: |
Chidambaran; Ravi;
(Canonsburg, PA) ; Bisht; Narendra Singh;
(Maharastra, IN) ; Raina; Pavan; (Maharastra,
IN) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Chidambaran; Ravi
Bisht; Narendra Singh
Raina; Pavan |
Canonsburg
Maharastra
Maharastra |
PA |
US
IN
IN |
|
|
Family ID: |
49156669 |
Appl. No.: |
13/838352 |
Filed: |
March 15, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61611806 |
Mar 16, 2012 |
|
|
|
61699524 |
Sep 11, 2012 |
|
|
|
Current U.S.
Class: |
210/638 ;
210/664; 210/710; 210/737 |
Current CPC
Class: |
C02F 1/52 20130101; C02F
1/56 20130101; C02F 9/00 20130101; B01D 9/00 20130101; B01D 3/00
20130101; C02F 1/441 20130101; C02F 2001/5218 20130101; B01D 1/00
20130101; C02F 11/12 20130101; C02F 1/66 20130101; C02F 1/04
20130101 |
Class at
Publication: |
210/638 ;
210/710; 210/664; 210/737 |
International
Class: |
C02F 9/00 20060101
C02F009/00 |
Claims
1. A process for purification of water for use in a boiler for a
steam flood process, comprising: collecting produced water
including an oil/water mixture from an oil well; separating and
recovering oil from the produced water; decreasing the pH of the
produced water by addition of acid; removing color, organics, and
silica from the produced water; adding a flocculent, including,
optionally, a coagulant and a polyelectrolyte, to the produced
water to aggregate solids in the produced water; removing solids
from the produced water, thereby producing sludge; conditioning and
disposing of the sludge; sending the produced water to an
evaporator, producing a distillate stream and a brine stream;
sending the distillate stream to a boiler for use as steam in
injection to an oil well.
2. The process of claim 1, wherein the pH of the produced water is
increased to between 9.5-10 after removal of color and organics and
before sending the produced water to the evaporator.
3. The process of claim 1, wherein between 60-80% of organics,
80-95% of color, and more than 25-50% of silica are removed from
the produced water in the color removing step.
4. The process of claim 1, wherein said brine stream is converted
to a solid through absorption with super absorbent polymer.
5. The process of claim 1, wherein said brine stream is neutralized
to a pH between 8.5 and 9 with the addition of acid and without
formation of a silica jelly.
6. The process of claim 1, further comprising sending a portion of
the brine stream to a crystallizer for removal of additional
distillate and production of a slurry.
7. The process of claim 1, further comprising, after the step of
conditioning and disposing of the sludge, the steps of: mixing the
produced water with at least one of magnesium oxide and magnesium
hydroxide; mixing the produced water with one or more of lime,
calcium oxide, and sodium hydroxide, thereby precipitating silica
from the produced water.
8. The process of claim 8, further comprising, after precipitating
silica from the produced water, removing the precipitated silica as
a second sludge; and conditioning and disposing of the second
sludge.
9. The process of claim 8, further comprising deaerating the
produced water after at least one of separation of the first sludge
and separation of the second sludge.
10. The process of claim 1, wherein said acid addition lowers the
pH of the produced water to between 3 to 5.
11. The process of claim 10, wherein said acid addition lowers the
pH of the produced water to between 4 to 4.5.
12. The process of claim 1, wherein said mixing the produced water
with one or more of lime, magnesium hydroxide, calcium oxide, and
sodium hydroxide adjusts the pH to between 10-11.5.
13. A process for preconditioning water for use in an evaporation
or reverse osmosis treatment, comprising: providing a water stream
including color; removing color, organics, and silica from the
water stream by the steps of: adding an acid; adding a color
removal chemical; and adding a flocculent to aggregate solids in
the water stream; removing the solids from the water stream;
increasing the pH of the water stream; and sending the produced
water to at least one of a evaporator and a reverse osmosis
unit.
14. The process of claim 13, wherein said produced water is sent to
an evaporator.
15. The process of claim 13, further comprising, prior to sending
the water to a reverse osmosis unit, softening the water.
16. A process for preconditioning water for use in reverse osmosis
or evaporative treatment, comprising: providing water comprising
silica, color, and organics; decreasing the pH of the water by
addition of acid; removing color, organics, and silica from the
water by addition of color-removal chemicals; adding a flocculent
to the water to aggregate solids in the water; removing aggregated
solids from the produced water, thereby producing sludge;
conditioning and disposing of the sludge; mixing the water with one
or more of lime, magnesium oxide, calcium oxide, and sodium
hydroxide, thereby precipitating additional solids; removing the
additional solids as a second sludge conditioning and disposing of
the second sludge; and sending the water to at least one of an
evaporator or reverse osmosis unit.
17. The process of claim 16, further comprising sending the water
to an evaporator.
18. The process of claim 16, further comprising, prior to sending
the water to a reverse osmosis unit, softening the water.
19. A process for purification of water for use in a boiler for a
steam flood process, comprising: collecting produced water
including an oil/water mixture from an oil well; separating and
recovering oil from the produced water; decreasing the pH of the
produced water by addition of acid; removing color, organics, and
silica from the produced water; adding a flocculent, including,
optionally, a coagulant and a polyelectrolyte, to the produced
water to aggregate solids in the produced water; removing solids
from the produced water, thereby producing sludge; conditioning and
disposing of the sludge; mixing the produced water with one or more
of lime, magnesium oxide, magnesium hydroxide, calcium oxide, and
sodium hydroxide, thereby precipitating silica from the produced
water; removing precipitated silica as a second sludge;
conditioning and disposing of the second sludge; sending the
produced water to an evaporator, producing a distillate stream and
a brine stream; sending the distillate stream to a boiler for use
as steam in injection to an oil well; and sending a portion of the
brine stream to a crystallizer for removal of additional distillate
and production of a slurry to achieve zero liquid discharge without
tar formation.
20. A two-stage process for silica reduction from water,
comprising: from a water stream comprising silica, water, and
organics, at least some silica with color and organics;
precipitating additional silica from the water stream by addition
of at least one silica-precipitating compound selected from the
group consisting of lime, magnesium oxide, magnesium hydroxide,
calcium oxide, and sodium hydroxide upstream of an evaporator or
reverse osmosis system.
21. The process of claim 20, wherein coprecipitation of silica with
color and organics reduces the amount of silica-precipitating and
overall process chemicals necessary to reduce silica to a desired
level.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority to U.S. Provisional Patent
Application No. 61/611,806, filed on Mar. 16, 2012, and to U.S.
Provisional Patent Application No. 61/699,524, filed on Sep. 11,
2012. Both of those applications are incorporated by reference
herein.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] Embodiments of the invention relate to processes for
purification of water.
[0004] 2. Background of the Related Art
[0005] Vertical tube falling evaporators are conventionally used
for recovery of produced water generated in steam flood processes
used for heavy oil extraction. The produced water is purified by
distillation and used for boilers for generating steam. The steam
is injected in the underground well to recover oil, which comes out
mixed with produced water. Oil is separated from water. During oil
extraction the produced water picks up significant amount of
dissolved solids including hardness and silica, and dissolved color
and organics. This is usually purified by distillation after
de-aeration and then taken for steam production again. During the
distillation a goal is usually for more than 95% water to be
recovered. The balance is discharged in salts caverns or injected
in deep wells.
[0006] This way overall consumption of water is optimized with
minimum make up losses. This process of producing oil is called the
"Steam Flood" or "Steam Assisted Gravity Drainage" Process (SAGD)
or "Cyclic Steam Stimulation" (CSS). The water treatment is a
critical part of this operation. The water treatment process
requires careful design to prevent or at least minimize scaling and
solid build up, to increase up time of operation, and to improve
reliability.
[0007] In existing evaporative water treatment processes for steam
flood, water is pretreated to remove oil and subsequently the pH is
raised to precipitate part of the hardness and keep silica in
dissolved form. The part of precipitated hardness remains in the
settlement tank and there is no carry-over of sludge in the
evaporation system. In such a process there are no solids in the
evaporation mixture and the distribution system. This water is
distilled to recover almost 95-97% water through vertical falling
film evaporators, and the residual brine is neutralized to reduce
the pH as per environmental regulations and discharged in salt
caverns or through deep well injections.
[0008] In another evaporative water treatment process, after oil
removal silica is precipitated with addition of magnesium oxide and
sodium hydroxide at alkaline pH, where silica is adsorbed on the
surface of magnesium hydroxide. In this process resultant
precipitated magnesium and silica sludge does not leave the system
when water is taken for evaporation. Sludge, including color and
organics as a part of water, is continuously re-circulated through
the evaporator through vertical tube falling film evaporators. This
risks settlement of part of the sludge in the distribution system
on a continuous basis. Over a period of time this may result in
formation of deposits on the surface of tubes and scaling of the
tubes.
[0009] After the distillation and recovery of 97% water the brine
is taken for neutralization. During the neutralization, most of the
silica exists in precipitated form, which may reduce chances of gel
formation but requires that all of the solids be disposed of with
brine, which make the process very expensive and consumes a lot of
capacity of salt cavern. Brine generated through this process is
not suitable for deep well injection without extensive treatment
for solids removal at this stage, where solids have sluggish
settling and filtration characteristics.
[0010] Unfortunately these processes have proven unsatisfactory for
a number of reasons. These include scaling of evaporator surfaces
and creation of a more chemically-intensive waste product for
disposal to underground wells or other areas.
BRIEF SUMMARY OF THE INVENTION
[0011] We offer an elegant solution that may simplify operations,
reduce possibility of down time, increase reliability and also
reduce the operating cost and disposal challenges of brine. Of
course, the invention is defined by the claims, and not by success
or failure in any one of the above criteria unless included in the
claims.
[0012] We provide a process suitable for the purification of
produced water from steam flood processes. Of course, while the
process that we provide is suitable for this use, it is not
necessarily limited to it, and those of skill in the art will
recognize that the general teachings and specific embodiments may
be put to use in other areas where color removal would be
beneficial.
[0013] Processes described herein may have, but are not required to
have, one or more of the following advantages over conventional
processes: [0014] 1. A majority of color contributing organics,
around 85-90%, are removed from the produced water in the first
step of the process, which helps in the reduction of 60-70% of TOC
(total organic content). [0015] 2. Around 95% of silica removal
from the produced water helps in prevent severe scaling in
downstream equipment. [0016] 3. Evaporator foaming is eliminated
and scaling is reduced to an insignificant level, as a majority of
dark, tar-like color chemicals, hardness and silica are removed
prior to evaporation. [0017] 4. Easy neutralization of brine water,
no jelly formation. [0018] 5. Easy sludge/solids disposal. [0019]
6. Lower chemicals cost & lower maintenance of evaporators
& crystallizers.
BRIEF DESCRIPTION OF THE FIGURES
[0020] FIG. 1 is a flow diagram illustrating an overview of a
process according to one embodiment of the invention for treatment
of produced water.
[0021] FIG. 2 is a flow diagram according to another embodiment of
the invention, showing a color removal process and further
treatment of water through an evaporator.
[0022] FIG. 3 is a flow diagram according to another embodiment of
the invention, showing color and silica removal processes and
further treatment of water through an evaporator.
[0023] FIG. 4 is a flow diagram of a conventional process for
produced water treatment as described in comparative example 1.
[0024] FIG. 5 shows flow diagram of conventional process of
produced water treatment as described in the comparative example
2.
DETAILED DESCRIPTION OF THE INVENTION
[0025] Unfortunately, existing processes fail to consider removal
of color and organics, and the need to do so has not heretofore
been recognized. Color in wastewater includes compounds with
electron-dense functional groups that adsorb light in the visible
spectrum. Color may also include organic products that are the
degradation products of decaying wood or other soil organic matter.
These products may have colloidal properties, as described in
"Coagulation and Flocculation in Water and Wastewater Treatment,"
by John Bratby (2.sup.nd Ed. 2008), which is incorporated by
reference herein and which also describes methods for measurement
of color. They may include, for example, fulvic, hymatomelanic, and
humic acids. These continue to pose foaming problems during
evaporation. They also make it difficult to go to a zero liquid
discharge ("ZLD") stage because of the concentration of color and
organic contaminants and the residual ZLD solids make the ZLD
product extremely tarry and difficult to handle for any subsequent
processing.
[0026] In a conventional process of neutralization of brine waste,
formation of a gelatinous substance takes place due to high
concentration of residual silica and precipitation of silica in
jelly form. This creates a substantial disadvantage for discharging
waste into salt caverns or deep well injections and makes such
discharge expensive. Presence of color and organics in sludge may
also adversely impact uniform distribution of feed water across
several tubes and may also call for frequent mechanical cleaning of
the evaporative system.
[0027] We report a novel process where disadvantages of existing
conventional water treatment processes may be overcome or
ameliorated. Although useful for steam-assisted gravity drainage
(SAGD), this process may also be suitable for other processes,
including for example pretreatment of feed water for a reverse
osmosis process. After removing color and/or silica the water may
be subject to further treatment to remove hardness before it is
taken to a reverse osmosis unit.
[0028] Embodiments include preconditioning of water. This removes a
majority of color forming compounds including organics. It also
removes potential scale forming contaminants with different
treatment processes before the water is sent for further treatment,
which may include treatment by an evaporation or membrane unit, as
well as solids removal.
[0029] A brief overview of an embodiment of the process may be had
by recourse to FIG. 1. As shown in FIG. 1, produced water 102 is
collected from an oil well 101 and then sent to an oil-water
separator 103. Oil is removed and recovered. The water stream 104
then proceeds for removal of color and organics in color/organics
removal tank 105. This is done by addition of an acid 106 followed
by addition of chemical for color removal 107 and a flocculent
108.
[0030] The stream then proceeds to a solids separator 109. Portions
of the stream are immediately disposed as solids after sludge
conditioning 110. If desired, the clarified or filtered stream 129
may then be sent directly to an evaporator 111 after adjustment of
pH to 9.5-10 or above.
[0031] More typically the filtered stream 129 flows from the solids
separator 109 to a mixer 112, where they are mixed with lime 113,
magnesium oxide 114, and sodium hydroxide 115. The stream 130, then
proceeds to a second solids separator 115, where a portion of the
stream 131 is removed for sludge conditioning 116 and disposal. The
reminder of the stream 132 proceeds to a de-aerator 117, then to an
evaporator 111. The purified distillate stream 118 from the
evaporator 111 proceeds to a boiler 119, where it is used to make
steam 120 for insertion into an oil well. At this stage the brine
121 can be neutralized 122 and disposed or brine with sludge is
absorbed in super absorbents and disposed of. In on embodiment the
super absorbent is Aquadux.RTM. 2212.
[0032] As an option, the portion of the evaporator 111 stream that
is not sent for use in a boiler 119, the brine 121, may be sent to
a crystallizer 124 for removal of additional distillate 125. After
this optional crystallizer step the slurry 126 is sent directly for
disposal or is sent for optional sludge conditioning and absorption
127, followed by disposal.
[0033] Embodiments of the invention may now be explored in more
detail. In an initial step of an embodiment of the invention, pH of
feed water 104 is adjusted to an acidic range of pH. Preferably the
pH is about 3 to 5, or about 4 to 4.5. This is accomplished with
the addition of an acid 106. Acid could be, for example, either
hydrochloric acid or sulfuric acid of suitable known concentration.
Acid addition is followed by addition of a color removing chemical
107 and a flocculent 108. Majority of the color is precipitated and
removed by filtration.
[0034] Typically this process reduces color by around 85-90% and
results in a TOC reduction of 60-70%. The color removal process
also gives a silica reduction of 15-30%. A color removal process
experiment's results are stated in Table 1 of Example-1.
[0035] Suitable color removing chemicals include but are not
limited to high molecular weight polymer coagulants, including the
polymer Wex-floc-9 (from WexTech) or similar color removal
chemicals from other suppliers. In one embodiment the compound is a
polyamine as reported, for example, in Yue, et al., (School of
Environmental Science and Engineering, Shandong University, China),
"Synthesis of Polyamine Flocculants and Their Potential Use in
Treating Dye Wastewater." The dosing of color removal chemical can
be modified depending on the concentration of color and organics in
the water to be treated. This concentration is often around 25-500
ppm, but typically around 50-100 ppm. The flocculent used in
preferred embodiments is AT 7594 or AT 7595 (WexTech). The dosing
is adjusted based on a jar test but it can vary between 0.25-5.0
ppm and mostly between 0.5-1.0 ppm.
[0036] After removal of color and associated organics and
filtration of the water, magnesium oxide or dolomite-like compounds
containing magnesium oxide are added under constant agitation in
mixer 112. By addition of magnesium oxide at this pH, performance
of the process improves over a conventional process such that
silica reduction improves to less than 10 ppm in the filtrate.
After this, pH is increased with predetermined quantities of lime
and sodium hydroxide to adjust the pH to about 10-11.5, preferably
about 11. Due to prior removal of color and silica the consumption
of caustic soda at this step is reduced significantly from the
amount necessary in the prior art. The amount of caustic soda may
be reduced by at least 25-30% as compared to the conventional
process.
[0037] The pH adjustment is followed by addition of a coagulant and
polyelectrolyte. This results in formation of precipitate in the
form of heavy flocks with very good settling properties. The
coagulant used at this stage was AT 7260 (WexTech) or equivalent or
similar chemicals supplied by other suppliers and dosing rate is
adjusted based on a jar test. This dosing rate can vary between 1-5
ppm but normally between 2-3 ppm.
[0038] After providing some settling time in solid separator 115,
the supernatant water 132 can be removed through decanting,
centrifuging or any other filtration process. This sludge has very
good settling properties and usually settles easily within 5-15
minutes. This sludge can be dewatered and sent for disposal after
further sludge conditioning 116 and compaction as required based on
local regulations. In this process most of the silica and calcium
and magnesium hardness are removed, and water is pre-conditioned to
go to the evaporation process without solids. The residual silica
in water is reduced to around 5-10 ppm from 240 ppm, and the total
hardness is also reduced to about 20 ppm.
[0039] The water after color removal process reduces silica in the
subsequent processing, reduces foaming during evaporation,
accelerates the silica precipitation during silica removal, and
provides easy to handle brine after the brine concentrator and
crystallizer treatments. This is highly unlike the highly viscous
and tarry liquid that is typically produced if there is no color
removal process to remove organics.
[0040] The supernatant liquid 132 is then taken for evaporation in
evaporator 111. In one embodiment evaporation is conducted in a
vertical falling film evaporator. In a preferred embodiment 95-97%
water 118 is distilled out and recovered. During distillation the
water remains clean with very little precipitates, and there is no
or effectively no build up or settlement of solids on the
distribution plates and no or effectively no deposition of solids
on tubes. Typically there is no scaling of any kind because the
majority of the total hardness is removed along with silica as a
part of precipitated solids.
[0041] The precipitated solids in brine are separated after
settling and taken for disposal after dewatering with the sludge,
which was separated along with silica and magnesium precipitates in
the first step.
[0042] The water 129 after the color/silica reduction step can be
directly taken for evaporation without filtration of solids, if the
solids concentration is not high after silica reduction and
precipitation because of additional silica reduction that has
happened along with color removal process. This is normally done if
the silica concentration in water is about 100 to 150 ppm though
that is not a requirement for this process. In that case the
re-circulating water during evaporation may need filtration to
maintain solids content during evaporation. In this case the color
removal process will make the neutralization and separation of the
salts easier during brine neutralization.
[0043] The brine 121 is taken for neutralization. In the
neutralization process there is no jelly formation. There is also
significant reduction in chemical consumption because most of the
acid-consuming ions do not exist in the brine. The brine 122 at
this stage is ready for disposal after separating any solids during
neutralization. The brine can also be disposed of without removal
of solids after neutralization 122 as required by local
regulations. Brine 121 can also be used for mixing with solids
after color removal step and/or silica removal step if the
preference is not to send any solids for disposal in land fill due
to local preference or constraints.
[0044] Alternatively the brine 121 can be further concentrated in
crystallizer 124 by recovering 75-80% of the balance water after
evaporation. The distillate 125 may be recycled for beneficial use.
The slurry 126 left in the crystallizer is either sent for disposal
after dewatering 127 or brine neutralization 122 or alternatively
converted into solids with super absorbents 123 and sent for
disposal. The resultant solid can also be incinerated if required.
The color removal step increases water absorption capacity of super
absorbents and makes such absorption faster. For analysis of color,
especially for highly concentrated solutions after evaporation, a
dilution method was used and the readings were adjusted based on
factors of dilution.
[0045] Embodiments of the invention may include one or more
deaeration steps. For example, deaeration may be used after color
removal and solid separation and before pH is increased. It may
also be used after a second-stage removal of silica. Typically
deaeration occurs after sludge removal.
[0046] The applicants stress that although the utility of color
removal in the steam flood process can not be underestimated, the
process reported herein may be equally useful when preceding a
reverse osmosis plant, with or without silica removal. It may also
be useful without silica removal, as a pretreatment followed by a
filtration process, like ultrafiltration and softening, to remove
any residual hardness.
Example 1
[0047] A color removal experiment was performed as per the initial
step of the embodiment shown in FIG. 2. To 3000 mL of produced
water was added 5.8 mL of a 10% sulfuric acid solution to reduce
its pH to 4.2. This was followed by addition of 100 ppm color
removal chemicals, Wexfloc-9 (30 mL of 1% Wexfloc-9 solution). A
mixing retention time of 15 minute was given and then 0.5 ppm of
flocculent (1.5 mL of 0.1% AT-7594 solution) was added to the
water. The heavy sludge settled within 5 minutes but treated water
was decanted after 30 minute for analysis. The results are shown in
Table 1.
[0048] The pH & conductivity were checked by laboratory
instruments. The color was analyzed as per APHA Platinum-Cobalt
standard method through a HACH DR/2010 spectrophotometer. The
silica was analyzed by silicomolybdate method through a HACH
DR/2010 spectrophotometer. TSS was analyzed through filtration and
gravimetric method as per APHA total suspended solids method. TOC
was analyzed through TOC Analyzer (Model: TOC-L CPH, Shimadzo
corporation).
TABLE-US-00001 TABLE 1 Color Removal Process Raw Produced Treated
Parameters water water Reduction pH 8.05 4.22 Conductivity,
.mu.S/cm 3130 3300 Color, PtCo unit 4260 360 91.55% TOC, ppm 389.6
145 62.78% Silica as SiO2, ppm 240 160 33.3% TSS, ppm 140 14
90%
[0049] It was evident that around 90% of color removal and 60% of
organics removal were easily achievable by this process. The
process further reduced around 33% of silica from the water.
Example 2
[0050] In another experiment produced water was treated as shown in
FIG. 3. The produced water was first treated with a color removal
process as described in Example 1. In the decanted treated water,
magnesium oxide was added with constant agitation. The water was
continuously mixed for 15 minutes, and then its pH was increased to
10 by the addition of lime. Finally the pH was further increased to
11 by the addition of sodium hydroxide. Then 2.5 ppm of coagulant
AT 7260 was added to the water and mixed for another 2 minutes. The
sludge settled within 15 minutes of retention time in a solids
separator, and supernatant treated water was decanted. A portion of
treated water was analyzed and results are shown in Table 2.
[0051] The pH & conductivity were checked by laboratory
instruments. The color was analyzed as per APHA Platinum-Cobalt
standard method through a HACH DR/2010 spectrophotometer. The
silica was analyzed by a silicomolybdate method through a HACH
DR/2010 spectrophotometer. TSS was analyzed through filtration
& gravimetric method as per the APHA total suspended solids
method. Hardness was checked by EDTA Titrimetric method. TOC was
analyzed through a TOC Analyzer (Model: TOC-L CPH, Shimadzo
corporation).
TABLE-US-00002 TABLE 2 Treated water Raw Produced (after Silica
Removal parameters water Removal Step) Efficiency (%) pH 8.05 11.21
Conductivity, .mu.S/cm 3130 3670 Color, PtCo unit 4260 650 84.74%
TOC, ppm 389.6 122 68.68% Silica as SiO2, ppm 240 8 96.67% TSS, ppm
140 6 95.71% Hardness as CaCO3, 35 20 ppm
[0052] The results clearly indicated that silica in treated water
by this process was below 10 ppm level, around 96.7% reduction was
achieved, and color reduction was around 85% and TOC reduction was
around 68.7%. It was seen that color values showed a higher reading
at alkaline pH.
[0053] A further set of tests was conducted on decanted treated
water of Example 2. Around 2600 mL of treated water was passed
through an evaporation set up and 97% of distillate recovered from
the treated water. During evaporation water pH was maintained
around 10-10.5 by sodium hydroxide. When the brine volume reduced
to 75 mL, a portion of it was analyzed for color and silica content
and their results are shown in Table 3. The pH and conductivity
were checked by laboratory instruments. The color was analyzed as
per the APHA Platinum-Cobalt standard method, and silica was
analyzed by a silicomolybdate method through a HACH DR/2010
spectrophotometer.
TABLE-US-00003 TABLE 3 Treated water Raw Produced (after silica
Brine parameters water removal step) water Water volume 3000 mL
2600 mL 75 mL pH 8.05 11.21 10.68 Conductivity, .mu.S/cm 3130 3670
153800 Color, PtCo unit 4260 650 3500 Silica as SiO2, ppm 240 8
300
[0054] During evaporation, no foaming was observed, which otherwise
is a common observation in the conventional process. No scaling was
observed on evaporator surfaces. The brine was clear, with a
significantly lower amount of precipitates. There was no tarry
appearance, because color units in the brine were still lower than
the color units in the original water.
[0055] A further set of tests was conducted on brine water. The
brine water (75 mL) was further concentrated up to 19 mL and
recovered 75% of water after evaporation and then the concentrated
slurry was neutralized to pH 9.0 by acid. No jelly formation
occurred on concentrated slurry, which was neutralized with 1.8 mL
of 5N hydrochloric acid. The slurry was analyzed, and results are
shown in Table 4. The pH and conductivity were checked by
laboratory instruments. The color was analyzed as per the APHA
Platinum-Cobalt standard method, and silica was analyzed by
silicomolybdate method through HACH DR/2010 spectrophotometer.
TABLE-US-00004 TABLE 4 parameters Concentrated slurry water Slurry
Volume 19 mL Sludge volume in slurry 25% Water volume in slurry 75%
pH value 9.0 Conductivity, .mu.S/cm 352500 Color, PtCo unit 22750
Silica as SiO2, ppm 975
[0056] The absorbance of neutralized slurry was checked on super
absorbent. The neutralized slurry, weight around 20 gm, was
absorbed on 1.25 gm of superabsorbent. The whole slurry was
absorbed on superabsorbent in two hour time period.
Comparative Example 1
[0057] In this comparative experiment the 3000 mL of produced water
was treated without color removal as shown in FIG. 4. The produced
water was first treated by magnesium oxide, lime, sodium hydroxide
and coagulant AT-7260. The produced water and dosing chemicals
quantity were similar as used in Example 2. It was observed that
the sludge settling rate was slow, and it settled in 2 hours of
retention time. The supernatant treated water was decanted and a
portion of it was analyzed for silica, color, pH and other
parameters. The results are shown in Table 5.
[0058] The remaining 2700 mL of treated water was passed through
evaporator for evaporation. In a similar fashion, 97% of distillate
was recovered from the evaporator, keeping the water pH around
10-10.5 in evaporator. The brine water volume was 80 mL. Results
are shown in Table 5. The pH and conductivity were checked by
laboratory instruments. The color was analyzed as per the APHA
Platinum-Cobalt standard method through a HACH DR/2010
spectrophotometer. The silica was analyzed by the silicomolybdate
method through a HACH DR/2010 spectrophotometer. TOC was analyzed
through a TOC Analyzer (Model: TOC-L CPH, Shimadzo
corporation).
TABLE-US-00005 TABLE 5 Treated water Produced (after silica Brine
parameters water removal step) water Water volume 3000 mL 2700 mL
80 mL pH 8.05 11.34 10.46 Conductivity, .mu.S/cm 3130 3340 154400
Color, PtCo unit 4260 1610 52100 Silica as SiO2, ppm 240 31 1460
TOC, ppm 389.6 225 --
[0059] In this comparative experiment, only 87% of silica, 62% of
color and only 42% of TOC reduction occurred in silica removal
process. During evaporation foaming and scaling were observed in
evaporator. The color of brine water of this comparative experiment
was almost 15 times greater than the brine color of a process using
an embodiment of the invention (Example 2) and silica content was
also 5 times larger than Example 2's brine silica.
[0060] The results of this comparative example clearly indicated
the significance of a color removal process as reported herein.
[0061] The brine water was further concentrated and distillate
recovery was attempted. Around 72% of water was recovered from
brine water during concentration. The brine water became a dark,
tar-like slurry. A portion of slurry was analyzed and results are
shown in Table 6. The pH and conductivity were checked by
laboratory instruments. The color was analyzed as per the APHA
Platinum-Cobalt standard method, and silica was analyzed by a
silicomolybdate method through a HACH DR/2010 spectrophotometer.
The slurry was neutralized by acid.
TABLE-US-00006 TABLE 6 Concentrated slurry water of parameters
comparative example-1 Slurry Volume 22 mL Sludge volume in slurry
75% Water volume in slurry 25% pH value 9.0 Conductivity, .mu.S/cm
313000 Color, PtCo unit 115000 Silica as SiO2, ppm 1890
[0062] The following disadvantages were observed during evaporation
of treated water and neutralization of concentrated slurry in the
Comparative Example 1 experiment. [0063] Foaming and scaling on
evaporator during evaporation due to excess color and silica.
[0064] More acid consumption as compare to the inventive process.
[0065] Foaming and jelly formation during neutralization due to
excess silica & other inorganic chemicals. [0066] Dark,
tar-like appearance of slurry. [0067] Less water recovery as
compare to the inventive process.
Comparative Example 2
[0068] In this comparative experiment, 2900 mL of produced water
was treated as in a conventional process like that shown in FIG. 5.
The color as well as silica removal process was not performed in
this experiment. The produced water was directly processed for
evaporation. The pH of the produced water was adjusted to 10-10.5
by sodium hydroxide and then the produced water passed through an
evaporator. Around 97% of distillate was recovered from the
evaporator. Significant foaming and heavy scaling were observed
during evaporation. A portion of brine water was analyzed, and
results are shown in Table 7. The pH and conductivity were checked
by laboratory instruments. The color was analyzed as per the APHA
Platinum-Cobalt standard method, and silica was analyzed by a
silicomolybdate method through an HACH DR/2010 spectrophotometer.
TOC was analyzed through a TOC Analyzer (Model: TOC-L CPH, Shimadzo
corporation).
TABLE-US-00007 TABLE 7 parameters Produced water Brine water Water
volume 2900 mL 85 mL pH 8.05 10.30 Conductivity, .mu.S/cm 3130
141000 Color, PtCo unit 4260 118000 Silica as SiO2, ppm 240
5120
[0069] In a further set of tests, an attempt was made to
concentrate the brine water further, but only 59% of distillate
recovery would be possible from brine water. It became a dark
colored tar-like slurry as its color were observed as 267000 PtCo
unit. This slurry contained a significantly lower amount of water
and was very difficult to neutralize by acid. A portion of the
water was analyzed, and results are shown in Table 8. The pH and
conductivity were checked by laboratory instruments. The color was
analyzed as per the APHA Platinum-Cobalt standard method through a
HACH DR/2010 spectrophotometer.
TABLE-US-00008 TABLE 8 Concentrated slurry water of parameters
comparative example-1 Slurry Volume 35 mL Sludge volume in slurry
90% Water volume in slurry 10% pH value 9.0 Conductivity, .mu.S/cm
298000 Color, PtCo unit 267000
[0070] In this Comparative Example 2, the following disadvantages
were observed during treatment: [0071] Significant foaming and
severe scaling on evaporator during evaporation due to excess of
color and silica in brine water. [0072] More acid consumption for
neutralization of slurry. Foaming and jelly formation during
neutralization due to excess color and silica contents. [0073]
Dark, tar-like appearance of slurry. Difficult to remove the
scaling and tar-like solids from vessel.
[0074] The advantages of various embodiments of the invention were
well-illustrated by a tabular comparison of the chemical
consumption necessary to treat 3000 mL of produced water in the
experiments discussed above. These numbers clearly showed the
reduction in chemical consumption in the pretreatment process and
also acid consumption before the final disposal process.
TABLE-US-00009 TABLE 9 Comparative Comparative Example-1 Example-2
Example-1 Example-2 Chemicals Description Experiment Experiment
Experiment Experiment Sulfuric Acid (10% Conc.) for color removal
5.8 mL 5.8 mL N/A N/A process Magnesium Oxide (solid, 97% pure) for
silica N/A 1.5 gm 1.5 gm N/A removal process Lime (solid, 90% pure)
for silica removal N/A 0.2 gm 0.341 gm N/A process Sodium Hydroxide
(10% Conc.) for Silica about 9 mL 8.3 mL 11.5 mL 12.9 mL removal
& evaporation process HCl (5N Conc.) for Brine Neutralization
N/A 1.8 mL 2.5 mL 3.5 mL process up to 9.0 pH Color Removal Polymer
Wexfloc-9 (1% Conc.) 30 mL 30 mL N/A N/A Polymer AT-7594 (0.1%
conc.) 1.5 mL 8.5 mL 7.5 mL N/A N/A--Not applicable
* * * * *